241 Am-Li(α,n) (AmLi) sources are well-suited for use within active interrogation neutron coincidence systems as uncorrelated neutron sources for measurements of 235 U or 233 U-bearing materials. Several dozens of such instruments, like the Active Well Coincidence Counter (AWCC) and the Uranium Neutron Coincidence Collar (UNCL), were produced to support the aims of international nuclear safeguards and non-proliferation efforts. Absolute comparisons between such coincidence detection instruments necessitate accurate source descriptions between uncorrelated sources. Over the last decade, the safeguards community has emphasized the need to establish robust AmLi source descriptions. Specifically, during the 52 nd Annual Meeting of the Institute of Nuclear Materials Management, both radiographic and gamma-ray spectroscopic examination of AmLi sources were called for. This paper presents the non-destructive assay of two AmLi sources used for detector characterization and benchmarking studies at PNNL, identified as MRC-101 and MRC-103. This study provides a detailed description of the configuration of 2724-BT encapsulated MRC sources. The first X-ray radiography-based images of MRC AmLi sources are reported here to verify the assumed inner source cavity volume of the 2724-BT encapsulation. A material phase difference was observed as a contrast change across the height of the source volume. The AmLi source material itself was estimated with indirect X-ray and gamma-based analyses to be between 0.3 g/cm 3 and 0.5 g/cm 3 . The intensity of the prompt gamma-rays resulting from the inelastic scatter of alphas on 7 Li was used to calculate a mass ratio of LiH:AmO<sub>2</sub> of about 16. The gamma-ray spectra also revealed the presence of numerous impurities ( 243 Am, 237 Np, 154 Eu, 23 Na, and 9 Be) within the sources. A neutron-gamma production ratio for AmBe was applied to the intensity of the Doppler-broadened peaks of prompt gamma-rays from alpha-induced reactions with 7 Li, 9 Be, and 23 Na to estimate neutron rates for both sources. Ultimately, an alpha fluence rate (derived in this work) was then related to the atomic density of these isotopes in the source volume to estimate their approximate masses. This work was supported by DTRA10027-30020. Distribution A, cleared for public release. Distribution is unlimited. PNNL-SA-151422
Year
2020
Abstract